Short-wavelength synchrotron radiation generated by relativistic electrons in circular accelerators has many applications for studying matter in all its forms. There is currently a high demand at synchrotron facilities world-wide to provide synchrotron radiation of various types for studying particular forms of matter. One of the distinctive characteristics of synchrotron radiation is warping of the globular non-relativistic dipole radiation pattern into a strongly forward peaked distribution, which makes synchrotron radiation highly collimated. Another distinctive characteristic is the shift of the spectrum of the radiation to higher photon energies (higher harmonics of the orbital frequency) as the electron energy increases, with the photon energy at the peak of the distribution varying as E3/R.
Spectral brightness of synchrotron radiation (the photon flux per unit area of the radiation source per unit solid angle of the radiation cone per unit spectral bandwidth) is frequently the most important consideration in experimental analyses that use synchrotron radiation. A beam that has high spectral brightness is highly collimated in both the horizontal and vertical directions. Undulators and wigglers are among the magnetic devices used to regulate the spectral brightness of synchrotron radiation sources. Undulators and wigglers are known collectively as “insertion devices” because they are inserted in the straight sections of synchrotron storage rings.
Undulators and wigglers consist of arrays of magnets of alternating polarity that repetitively bend electron beams back and forth (Schlueter, R. D. (1994), Wiggler and undulator insertion devices, in Synchrotron Radiation Sources: A Primer, Herman Winick, Ed. World Scientific, Singapore, pp. 377–408; Als-Nielsen, J. et al. (2001) Elements of Modern X-Ray Physics, Chapter 2: Sources of X-rays, John Wiley and Sons, Chichester UK). A common type of insertion device, the planar undulator, is an array of closely spaced, vertically oriented dipole magnets of alternating polarity. As the synchrotron's electron beam passes longitudinally through the magnetic array, its trajectory oscillates in the horizontal plane. Because the magnetic field produced by the undulator is relatively weak, the radiation cones emitted at each bend in the electron beam's trajectory overlap, giving rise to constructive interference that results in one or a few spectrally narrow peaks (a fundamental and harmonics). Thus the electron beam produced has high spectral brightness, i.e., it is highly collimated in both the horizontal and vertical directions, and it is highly coherent as a result of the periodicity. Tuning the wavelengths of the harmonics is carried out by mechanically adjusting the vertical spacing (gap) between the pole tips of the magnets (X-Ray Data Booklet, January 2001, Center for X-Ray Optics and Advanced Light Source, Lawrence Berkeley National Laboratory, University of California, Berkeley Calif. 94720).
An accurate characterization of the magnetic field produced by an insertion device is essential to the design and maintenance of precise X-ray generation, particularly in the case of undulators. Such characterization of the magnetic field usually consists of a volumetric map of the magnetic field strength (B magnetic-field vector) taken every millimeter in the X-, Y- and Z-axes. Some laboratories have dedicated equipment solely for this purpose. Great precision is required, both in the sensitivity of the magnetic field measurement and in the positioning of the sensor at the location where the measurement is to be taken. Such precise positioning is frequently difficult to achieve, owing to the length of the insertion devices, their great weight, and the close alignment requirements between the insertion device and the apparatus. Moving the measurement equipment to the work site when characterization is required is also difficult. Currently, to characterize the magnetic field of the insertion device, the insertion device must be removed from the synchrotron storage ring. This can entail considerable labor and expense if it must be removed from the ring and transported to a remote site for measurement and testing. As the insertion device is being moved to and from the remote testing site, it runs the considerable risks of misalignment and/or damage. Hence, there is a considerable need in the art for equipment for measuring the magnetic field produced by an insertion device that is easy to move and/or install in a location proximate to the insertion device.
Citation or identification of any reference in Section 2, or in any other section of this application, shall not be considered an admission that such reference is available as prior art to the present invention.